Methods and devices for measuring quantitative airway carbon dioxide (CO2) gas exchange concentrations and respiratory rate of a subject's breath (capnometry) are well known in the clinical markets. In fact, the use of capnometry during intubated surgical and otherwise critical ventilated patient situations is mandated by standards organizations because it is critical in maintaining safety. By far the most common technology used in commercial instruments is IR spectroscopy because of its accuracy, precision, speed of response and reliability. Infrared absorption spectroscopy capnometers quantify the subject's airway CO2 gas exchange in real time without any airway perturbation or violation of sterility. Unfortunately, this utility requires substantial technological complexity and a high price when compared with other common medical parameter measurements such as temperature, blood pressure, ECG, heart rate and pulse oximetry. Now that the use of capnometry has expanded outside the in-hospital environment to pre-hospital emergency care including non-intubated subject monitoring applications such as dentistry, pain management, conscious sedation, in-home use, etc., there is an increased awareness of the need for less expensive capnometry instruments.
There are many other techniques for measuring gas exchange in a subject's breath. Among these include mass spectrometry, Raman scattering, photoacoustic, piezoelectric, paramagnetic and chemical based instruments. All of these techniques have specific tradeoffs with respect to their complexity, performance and cost. In examining the aspects of these tradeoffs, one technique stands alone as having potential for simplicity, meeting adequate performance criteria at considerably lower cost than other methods; the chemical based colorimetric technique.
Chemical based colorimetric techniques have been utilized in many other applications including qualitative human breath CO2 measurement. However, one of the challenges in using colorimetric techniques is its ability to achieve sufficient response time to capture rapidly changing CO2 concentrations such as is found in a subject's ventilation pattern. Commercially available airway colorimetric products first appeared in the late 1980's, but could only give relative qualitative indications of CO2 concentrations due to their slow response. In the 1990's, improvements to the indicator chemistry formulations were made to enhance the speed of response to breath-by-breath gas concentration variations. For example, in 1994 Dr. Andras Gedeon published test results of a colorimetric indicator compared with an IR spectroscopy based capnometer showing significant similar breath-by-breath response. Details regarding these test results are described in the paper “A New Colorimetric Breath Indicator (Colibri)” published in Anaethesia (1994) volume 49, pages 798-803, which is herein incorporated by reference in its entirety. Since then, Dr. Gedeon and others have also developed and manufactured qualitative colorimetric indicators primarily for use with intubation verification.
Although much has been done to improve chemical based colorimetric techniques, there remains a need for a low cost quantitative CO2 device that provides fast and accurate continuous measurement of a subject's breath-by-breath CO2 levels. Moreover, there is a need for a portable device that can be used by patients at home or otherwise to monitor CO2 levels as part of a treatment protocol. As such, the embodiments described herein provide devices, systems, and methods for addressing at least these concerns. For example, some embodiments provide for electro-optical techniques instead of visual interpretation to detect the color change from CO2 concentrations. Other embodiments provide for devices or systems that display continuous calibrated CO2 concentrations and respiratory rates using colorimetric indicator chemistry. Additionally, methods and devices contemplated herein include new techniques for user calibration and unique patient attachments or patient interface for various clinical applications to allow quantitative monitoring of a spontaneously breathing (non-intubated) subject with a completely robust, portable, very low cost, low power instrument. The simplicity of this instrument is suited, at least, for the technology-unsophisticated, home-based user.
In addition, some embodiments described provide examples of breathing therapy for treating any number of disorders including panic disorder, hypertension, post-traumatic stress disorder (PTSD), asthma etc. Although breathing therapies or methods (e.g. yoga and meditation) have been used in the past as ways to reduce anxiety or hyperventilation, such breathing techniques are focused primarily on relaxing or calming the practitioner and not on modifying carbon dioxide levels during respiration for treatment. In particular, previous techniques have not used a quantitative colorimetric carbon dioxide system for therapy. As such, the quantitative colorimetric devices and systems described herein can be used to provide breathing therapy treatment by, for example, helping patients modify end-tidal CO2 levels to help treat panic disorder, PTSD, anxiety, general anxiety disorder, obsessive-compulsive disorder, social phobia, depression, apnea, migraines, epilepsy, asthma, hypertension, conscious sedation, emergency medical services (EMS), etc.